The present invention relates to a diffraction grating, an optical disc pickup device and an optical disc apparatus.
There have been issued, for instance, Patent Document 1 (JP-A-2004-281026) and Patent Document 2 (JP-A-2006-31913) as background technologies in the field of art according to the present invention.
The Patent Document 1 (JP-A-2006-31913) discusses therein, in view of its task, “A variation in the amplitude of a TE signal is defined to ΔPP=(Amplitude a−Amplitude b)/(Amplitude a+Amplitude b), and in the case of detection of a TE signal in the above-mentioned conventional configuration, there are exhibit large values, that is, a variation value APP is 0.69 while a deviation Oft1 is +33 nm and a deviation Oft2 is −33 nm. In this case, should the variation value ΔPP in the amplitude of the TE signal be excessively large, the gain of tracking control would be lowered on tracks Tn−1, Tn, that is, the tracking control would be unstable. Thus, there has been raised the problem that data cannot be recorded or reproduced with a high degree of reliability”, and proposes as solving measures “A further another optical data apparatus according to the present invention, comprises a light source for emitting an optical beam, a light focusing means for focusing an optical beam emitted from the light source onto an optical recording medium having tracks, a branching means for branching the optical beam reflected on and refracted by the optical recording medium, a splitting means for splitting the thus branched beam by a plurality of areas, a light detecting means having a plurality of detecting areas, for detecting light beams split by the splitting means so as to deliver current signals depending upon thus detected light quantities, a plurality optical conversion means for converting the current signals delivered from the light detecting means, into voltage signals, the plurality area arranged in the splitting means comprising a first area mainly including tracking error signal components, and a second area mainly including offset components of the tracking error signal components, and a tracking error signal producing means for producing a tracking error signal by subtracting from a voltage signal obtained in the first area, a value obtained by multiplying a voltage signal obtained in the second area with a coefficient, characterized in that the efficiency of the light beam passing through the second area and transmitted to the light detecting means is high in comparison with that of the light beam passing through the first area and transmitted to the light detecting means”.